Various solutions have been proposed for the installation of Venetian blinds on horizontal or inclined surfaces such as ceiling skylights and pitched walls, and on curved surfaces, including fixed blinds which are not retractable but tiltable and retractable blinds which are tiltable but supported by a tensioned wire or rods, as known in the art.
Many fixed blinds generally involve complicated mechanical systems merely to open or close the slats by tilting, but not to retract or extend the entire blind over the window surface. Such fixed blinds make it practically impossible to clean the window adjacent thereto, without removing the entire installation. Other blinds suspended by rods or wires, even though retractable have further limitations.
When the glass to be covered by the blind is in the ceiling of a greenhouse, or a skylight having a pitch of say 30.degree. to 40.degree. from the horizontal plane, or indeed, is disposed in a horizontal installation, the mere use of a supporting wire or rod through the slats is not sufficient to assure optimum performance of the blind.
On the other hand if conventional means are employed for suspension of the blind in such installations, the slats, upon adjusting the same to a closed position in the conventional mannerfor closing the blind, reach a point where the weight of the slats will cause them to "flop" closed or to remain closed and hang on the cross rungs of the ladder ordinarily used to open and close the same, even if the slats are supported by a guy wire or other means of support.
In view of the foregoing, it has not heretofore been possible to effectively design a Venetian blind that is fully retractable on window surfaces which are horizontal or of such low pitch as indicated above and which is capable of achieving the performance demanded for such installations.
Accordingly, it is an object accomplished by this invention to provide a Venetian blind which is both tiltable and retractable for windows which are horizontal or of relatively low pitch.
The provision of a Venetian blind for greenhouses defined by curved walls connecting with a pitched ceiling and merging into vertical side walls thereof also presents problems not heretofore completely solved by the prior art.
If a conventional Venetian blind is suspended inside an arcuate surface, the closing angle of the slats will change with the arc of the surface, thereby causing unacceptable slat closure. Desirably, complete closure of the slats should be achieved over the entire area of the arcuate surface as well as the vertical portion of the blind when the tilt mechanism is adjusted to a closed position. This just does not happen with conventional suspension systems, whether they include curved rods or the like passing through the slats, due to the fact that unequal forces are applied to the front and back legs of each of the ladders supporting the blind slats.
Accordingly, another object of the invention is accomplished by providing, secondly, an improved retractable blind adapted to cover a curved surface merging into a vertical surface.